Flash for Rolleiflex

I am looking to do some flash work with my older Rolleiflex which has only a sync cord connector and no hot shoe. I have a Metz 20C2 which works well, but wonder if there are any other more powerful units which use a sync cord and are not hot shoe dedicated. Thanks.

I have 2 rolleis, an automat from the fifties and a cord from around 1960, and I have been using an old viviter 283 which for me has power in plenty, you an pick them up for a song today, or even better the 285.
Richard

On my twinlens I use the e36re because it attaches to the pistol grip. The e36re is also nice because it lets you use a synch cord that locks at both ends.
I also can say the Nikon SB-28 works well as a conventional non-TTL auto flash. I use that one more with the Rollei SLRs because the SB-28 has an adjustable field of coverage that works well with the 50 and 40mm lenses.